Methane Lidar Transmitter Development for Space

The objective of this work is to advance the technology readiness level (TRL) of lidar system to enable global Methane (CH₄) and water vapor (H₂O) measurements with sufficient coverage, sensitivity, and precision to address pressing science questions for climate-carbon interaction.  Methane (CH₄) is the second most important anthropogenic greenhouse gas with approximately 25 times the radiative forcing of CO₂ per molecule.  Natural sources of CH₄ are dominated by wetland emissions in the tropics and Arctic and sub-Arctic boreal regions, with additional contributions from termites, ruminants, ocean biology, and a geological source of unknown significance. Natural sources account for about one-third of the emission total. The wetland source is particularly variable, linked to temperature, precipitation, and surface hydrological changes. Better characterization of the wetland source clearly requires reliable CH₄ measurements in the often-cloudy tropics and over partially inundated land surfaces and open water. Another important science question is in the potential release of large amounts of stored organic carbon as CH₄ and CO₂ from thawing Arctic permafrost soils, which is cause for concern as a rapid, positive greenhouse gas/climate feedback.  In addition, large but greatly uncertain amounts of CH₄ are sequestered as gas hydrates in shallow oceans and permafrost soils, which are also subject to potential rapid release. Although these boreal, phase-change driven sources are not yet estimated to be large, their potential magnitude and rapid growth dictate that measurement systems need to be put in place for early detection.  Because CH₄ fluxes, as well as chemical loss, are tightly coupled to hydrology, coordinated measurement of both CH₄ and H₂O are highly desired. Precise, seasonal measurements with coverage at high latitudes (i.e., in low sun to dark conditions) are required.  Our proposed laser remote sensing technology will be a key step in fostering measurements of CH₄ and H₂O with sufficient coverage, sampling, and precision to address major science questions.

Our proposed laser remote sensing technology will be a key step in fostering measurements of CH₄ and H₂O with sufficient coverage, sampling, and precision to address these and other science issues. The benefit to future Earth Science missions is that the proposed technology enables global CH₄ measurements to be made where they are really needed: in the absence of sunlight (i.e., at night and at high latitudes in all seasons), in the presence of scattered or optically thin clouds and aerosols, over land and water surfaces, and with higher accuracy and precision than currently available. These qualities are precisely those that make the corresponding H₂O measurements a valuable addition to the current operational suite for weather and climate analysis.  The measurements will help satisfy the critical scientific need to understand the behavior of greenhouse gases as they contribute to climate change as well as to meet pressing national needs for development of a national carbon monitoring system serving science, policy-makers, and stakeholders.

The end goal of the project would be to demonstrate the readiness of the a CH₄ trace gas lidar instrument for space flight. The target wavelengths and energies are ~1.65 µm and energy is ~500 µJ.  The specific objectives of this project are to:

1. Improve the tunability architecture of the seed laser(s) using two different designs.
   1. The first design uses a DBR laser at 1651 nm to be delivered under an STMD Game Changing Technology program.
   2. The second design uses a novel approach: single or dual sideband (SSB/DSB) tuning. It has the potential to significantly simplify the seed laser design and uses existing DFB lasers.
2. Demonstrate 500 µJ in Er:YGG/Er:YAG with narrow linewidth.
3. Reduce the size and complexity of the existing OPO
4. Use the tunable seed from objective 1 with the OPO and Er:YAG from objectives 2 and 3  to demonstrate open path CH₄ measurements and correlate them with an in-situ calibrated instrument (Picarro in-situ CH₄ analyzer).